Polyphosphazenes, a type of "inorganic rubbers" having the general formula --N.dbd.P(X).sub.2 --.sub.n, are generally prepared by heating at 200.degree. to 300.degree. C. cyclic oligomers of the above formula in which n is equal to 3 or 4. The resulting polymers, in which X stands for a halogen atom, are then rendered stable in the presence of water by reaction with sodium, potassium, magnesium, calcium, or lithium alcoholates or phenolates, thus substituting alkoxy and/or aryloxy groups for the halogen atoms of the polymers (e.g., U.S. Pat. Nos. 3,370,020; 3,880,800 and 3,883,451). Interestingly, when the substitution of the halogen atoms with --OR groups is done at the oligomer stage, the compounds obtained can no longer be polymerized.
Various lower alkyl groups and alicyclic groups have also been substituted for some of the chlorine atoms of dichlorophosphazene oligomers, for instance by irradiating tetrameric Cl.sub.2 PN in decahydronaphthalene to obtain (C.sub.10 H.sub.17)Cl.sub.7 P.sub.4 N.sub.4. As far as is known, however, none of the low melting materials so obtained have been polymerized. A list of compounds of this type can be found in Cotton (Ed.), "Progress in Inorganic Chemistry," volume IV, page 321 (1962).
As to carborane-substituted polyphosphazenes, none have been reported so far. In fact, the only known carborane-substituted inorganic polymers have been obtained by a Grignard type reaction involving a bromoalkylcarborane and an alkenyl bromide to form an alkenylcarborane which is then allowed to react with a silane to yield a carboranyl-substituted silane monomer. This compound is then polymerized to a carboranylpolysiloxane (U.S. Pat. No. 3,431,234).
The state of the art remains such, however, that no instance of direct attachment of a carboranyl group to a phosphorus atom has been reported, either in a small molecule or in a polymeric specimen.
The principal object of this invention is to provide a method by which carboranyl substituents can be placed on a polyphosphazene molecule.